1. Field of the Invention
The present invention relates to novel compositions and methods for bleaching metals in photographic materials. More particularly, the present invention relates to novel bleaching agents and their use in aqueous and nonaqueous photographic materials. One of its aspects relates to novel bleaching solutions which are capable of bleaching preformed or predeveloped silver in aqueous and nonaqueous photographic materials. Another of its aspects relates to novel bleaching agents for incorporation into radiation sensitive elements, particularly photothermographic elements, for converting metallic image silver in said elements to a colorless product.
2. Description of the Prior Art
In the processing of many photographic silver halide color elements and in some black-and-white photographic processes, it is necessary to remove metallic silver formed during development. This is ordinarily accomplished by the use of a silver bleaching composition which converts metallic silver into a soluble silver salt. A bleach commonly used for this purpose is an aqueous solution of a water-soluble ferricyanide, such as sodium or potassium ferricyanide, and an alkali metal bromide. Aqueous bleaching solutions comprising aromatic nitroso bleaching agents are described in U.S. Pat. Nos. 2,625,477 (Sawdey), issued Jan. 13, 1953; and 2,705,201 (Tulagin), issued Mar. 29, 1955. U.S. Pat. No. 3,707,374 (Van Der Voorn et al.), issued Dec. 26, 1972, relates to aqueous bleaching solutions comprising water-soluble persulfate salts or water-soluble nitrosodiumsulfonate salts and aromatic amines.
Combined bleaching and fixing compositions for use in photography, commonly referred to as bleach-fix compositions, have been known for many years. They are used in processing silver halide photographic materials to simultaneously accomplish the steps of bleaching and fixing and thereby eliminate one step in the conventional processing procedure. The essential components of a bleach-fix composition are the bleaching agent, i.e. an agent which oxidizes the metallic silver in the silver image to a soluble form, and the fixing agent, i.e., an agent which dissolves the undeveloped silver halide and the silver salts formed by the action of the bleaching agent. U.S. Pat. No. 3,189,452 (Bard et al.), issued June 15, 1965, described aqueous bleach-fix compositions prepared by combining conventional bleaching agents such as alkali metal dichromates and alkali metal ferricyanides with conventional fixing agents such as alkali metal thiocyanates. Other known aqueous bleach-fix solutions include those described in U.S. Pat. No. 3,615,508 (Stephen et al.), issued Oct. 26, 1971; U.S. Pat. No. 3,634,088 (Cooley), issued Jan. 11, 1972, wherein the solutions comprise a ferric salt of an aminopolycarboxylic acid as a bleaching agent and a thiosulfate as a fixing agent; U.S. Pat. No. 3,706,561 (Mowrey et al.), issued Dec. 19, 1972, wherein ferric ion-ligand complexes are used as bleaching agents and thiosulfates, thiocyanates, thioethers, or thioureas are used as fixing agents; and U.S. patent application Ser. No. 389,063 (Mowrey), filed Aug. 16, 1973.
U.S. Pat. No. 3,034,893 (Bruenner), issued May 15, 1962, relates to the use of particular disulfide salts in aqueous photographic bleach baths as oxidizing agents and complexing agents for silver ions, rendering the resulting silver complexes water-soluble. U.S. Pat. No. 3,241,966 (Heilmann et al.), issued Mar. 22, 1966, relates to aqueous bleach-fix solutions comprising polyalkylene oxides wherein some of the ether linkages have been replaced by disulfide linkages.
Silver-dye-bleach processes are well known, having been described, for example, in J. S. Friedman, History of Color Photography, pages 405-429 (1944) and A. Meyer, The Journal of Photographic Science, Vol. 13, pages 90-97, (1965). These processes involve developing a silver halide emulsion containing a bleachable dye, and bleaching the dye in just those areas where the silver has been developed. All of the silver ion is removed or rendered transparent and insensitive to light, leaving a dye image in the areas where no metallic silver was present. Typical silver-dye-bleach elements and processes are disclosed in U.S. Pat. No. 3,414,411 (Michel et al.), issued Dec. 3, 1968 and in U.S. Pat. No. 3,904,918 of Mowrey et al., issued Sept. 9, 1975.
It is also well known to develop a latent image in a photothermographic element using thermal processing. After imagewise exposure, the resulting latent image in the photothermographic element is developed and, in some cases, stabilized, merely by uniformly heating the photothermographic element. Such materials and process are described, for example, in U.S. Pat. No. 3,152,904 (Sorensen et al.), issued Oct. 13, 1964; U.S. Pat. No. 3,301,678 (Humphlett et al.), issued Jan. 31, 1967; U.S. Pat. No. 3,392,020 (Yutzy et al.), issued July 9, 1968; U.S. Pat. No. 3,457,075 (Morgan et al.), issued July 22, 1969; British Pat. No. 1,131,108 published Oct. 23, 1968; German Pat. No. 888,045 issued June 29, 1943 and British Pat. No. 1,161,777 published Aug. 20, 1969. Certain photothermographic materials for producing an image in color are also known as described, for example, in U.S. Pat. No. 3,531,286 (Renfrew), issued Sept. 29, 1970 and U.S. Pat. No. 3,761,270 (deMauriac et al.), issued Sept. 25, 1973.
U.S. application Ser. No. 642,928 of Cerquone et al., filed Dec. 22, 1975 now U.S. Pat. No. 4,021,240 relates to photothermographic and thermographic elements, compositions and processes for providing a developed image in color. There is no teaching or suggestion in this application of the present invention.
Copending U.S. application Ser. No. 662,403 of Mowrey and Oftedahl, filed Mar. 1, 1976 now abandoned relates to an activator sheet for a dry thermal silver dye bleach process. The sheet comprises a support, a diffusible mineral or organic acid and a non-hydrolyzable polymeric vehicle. This application does not teach or suggest the present invention.
Applicants are aware of no prior art which teaches or suggests the present invention. It is an object of this invention to provide bleaching solutions and radiation sensitive elements, particularly photothermographic elements, comprising novel thiyl bleaching agents. These bleaching agents provide the following advantages over the bleaching agents of the prior art:
1. The thiyl bleaching agent precursors may be incorporated in photographic elements without adversely affecting the photographic properties of radiation sensitive emulsions and may be thermally activated;
2. They are capable of bleaching preformed or predeveloped silver in both aqueous and nonaqueous photographic materials;
3. They are effective in converting metallic image silver to a colorless product by a dry thermal process; and
4. They are biodegradable and easily destroyed by ozonolysis, lessening environmental pollution.
Nonaqueous photographic materials used in the practice of the present invention include those in which a radiation sensitive element is contained in a water-insoluble or a water-impermeable binder. Exemplary of these materials are photothermographic elements adapted for dry physical development which contain poly(vinyl butyral) or another suitable binder.
Aqueous photographic materials include those in which a radiation sensitive element is contained in a water-soluble or a water-permeable binder, such as hydrophilic proteinaceous colloids like gelatin. Examples of these materials can be found in Product Licensing Index, Vol. 92, December 1971, Publication 9232, pages 107-110, published by Industrial Opportunities Ltd., Homewell, Havant Hampshire, P09 1EF, UK.